1. Field of the Invention
The present invention generally relates to the field of tagging of objects and people with radio transponders, and more particularly to an improved system and method for determining the location of tagged objects.
2. Description of the Related Art
There is a class of businesses in the world economy that focus on the movement of physical objects from a pre-specified place at a pre-specified time (the pickup) to a pre-specified place at a pre-specified time (the drop-off). The objects being transported may vary dramatically in size (from an envelope to a train locomotive) and may vary dramatically in the environmental restrictions that the object can endure without damage during the time between pickup and drop-off. Any business that performs this type of service can benefit from knowing the attributes (both the space-time location and environmental) that each object will experience (predictive), is experiencing (near real time) or has experienced (logged).
There are several approaches that are currently employed in this and related industries that involve instrumenting each object, instrumenting selected objects, instrumenting test objects whose sole purpose it is to mimic a real object and infer from the handling of the test object what a real object will experience. Such instrumentation may be associated with the object from pickup to drop-off, or, may be associated for only a portion of the pick-up to drop-off such as an instrumented tub that contains an object. In such cases, onboard tub instrumentation will be taken as representative of the object's space-time-environmental conditions during the period of time the object is bonded to the tub. Such approaches require a system that provides logical association and disassociation with temporarily bonded instrumentation.
Another common approach is to instrument the path that objects will follow and associate a space-time position and appropriate environmental measurement with the objects as they encounter various points in the instrumented path. Such measurements may be strung together to infer the space-time-environmental conditions experienced by each object. This second approach (instrumenting the path) has the considerable advantage of minimizing the investment for each object, since the cost of instrumenting the path can be amortized over all monitored objects that transverse the path. Finally, combinations of all these approaches can be used. The final decision about which methods to employ is typically made based on a cost/benefit basis
There are many cases where knowledge of an object, or package, location can improve existing processes. Some examples of these processes are:                Movement of packages from a pickup point to actual delivery point.        Movement of packages through a sorting facility.        Movement of packages on loading docks, to ensure packages are placed in the correct container/vehicle        Placement of goods in warehouse or stockroom.        
In the case of transportation companies, for each package or container there is knowledge of its destination as well as the corresponding routing information. However, a package may be placed on the wrong vehicle during transportation and not follow the optimum route to its destination. Thus, the potential for missing a committed delivery schedule exists, which may result in the transportation company providing refunds to customers and further have a negative impact on customer satisfaction and customer retention for the transportation company.